The subject of this project is the mechanism of synaptic transmission in the vertebrate retina and its role in the processing of visual information. Intracellular recordings will be made from individuals neurons in the retina of the mudpuppy, Necturus maculosus. The synaptic inputs to ON-and OFF-center ganglion cells will be studied by measuring the current-voltage properties of these cells during darkness and steady illumination, and during superfusion of the retina with various transmitter substances, specific pharmacological antagonists to these substances, and ionic substitutions of the bathing medium. Previous work in this laboratory has shown that both ON- and OFF- center ganglion cells receive tonic excitatory and inhibitory input in darkness. We are now studying how these inputs are altered by illumination to produce the characteristic light responses of these cells. Specific items under study are 1) The identification of the transmitter substances which mediate these different inputs 2) the postsynaptic mechanisms by which these transmitters act 3) the identify of the presynaptic neurons which are the source of these inputs. These studies are part of the long-term goal of understanding the functional organization of the retina.